Knee Joint Line Deformity Sources of Malalignment

Abstract

Thus far, we have considered malalignment due to femoral and tibial deformities and due to joint laxity and subluxation between the femur and tibia. The other remaining sources of malalignment are bone and cartilage loss from the knee joint surfaces. The most common of these is cartilage loss from the medial or lateral knee compartments. The effect is to increase the JLCA because the femoral and tibial joint line surfaces are no longer parallel. This should not be mistaken for collateral ligament laxity. Although they are often found together, they need to be distinguished from each other. Both are assessed by means of stress radiographs. The minimum and maximum cartilage space is measured for both medial and lateral sides from the stress radiographs (►Fig. 15-1 and see Fig.14-8). If an increased JLCA is identified as being due to loss of cartilage height, this component of angulation must be incorporated into the total magnitude of angular correction. In realignment of the tibia in cases with increased JLCA, the distal femur can be used as the knee joint line (►Fig. 15-2). Similarly, for a femoral deformity, the tibial joint line can be used as the knee joint line for purposes of planning.